The condensation of 2-amino-6-chloropurine (I) with ethyl 4-bromo-2-hydroxybutyrate (II) by means of K2CO3 in DMF gives ethyl 4-(2-amino-6-chloropurin-9-yl)-2-hydroxybutyrate (III), which 8-hydrolyzed with refluxing aqueous HCl yielding 4-(9-guanyl)-2-hydroxybutyric acid (IV). The esterification of (IV) with ethanol - HCl affords the corresponding ethyl ester (V), which is finally reduced with NaBH4 in refluxing isopropanol.